Answer: FalseExplanation: High effecient equipment is now normally a condensing cumbustion system and will need to be vented with PVC pipe. Where you may use the old chimney as a chase I prefer to run a didicated flue, sometimes horizontally.

Answer: TrueExplanation: Because more of the heat is being absorbed by the boiler and less wasted up the chimney, the higher efficiency the gas appliance the greater chance that it will condense in the chimney as it meets the cold air. This becomes a big problem for clay lined chimneys, as it will damage them over a period of time. Typically the chimney is lined or the appliance is direct vented outside and the existing chimney is not used.